One of the most promising solutions to the problems of achieving improved mileage-to-the-gallon of gasoline on the internal combustion powered road vehicle is the use of the variable stroke engine.
This allows the effective swept volume of the engine to be varied to meet the driving requirements of the moment so that full stroke, and thereby full piston displacement, is available for such full power needs as acceleration, climbing and high speed running conditions and permits shorter stroke, lesser piston displacements to be used for cruising, idling or start-up conditions. A secondary, but equally important advantage is the reduction of the compression ratio as the stroke is shortened, thus reducing pumping pressures during the compression and exhaust strokes of a four cycle engine and during start-up operations, thereby minimizing loads on the engine starter motor and on the storage battery, permitting these components to be reduced in size and weight as well as in cost. Other benefits include reduced piston speeds, with a consequent reduction in wear and lower exhaust emission mass flow resulting from the lower induced mass flow in the shorter stroke mode.
The methods of producing such a variable stroke engine, at present under consideration and development are, in fact, modifications to the existing concept of the crankshaft engine and consist of such approaches as the interposition of a secondary linkage between the crankshaft and the piston rod adjusted by means of screws, and the use of variable height pistons, all of which have the effect of varying the stroke without changing the swing diameter of the crankpin. As a result there occurs a diminution of mechanical efficiency resulting in the absorption of kinetic energy in the driving of a mechanical system designed for a basic function different to that which is being applied, in addition there is an increase in complexity, weight and cost of the engine.
This invention is based on the philosophy that, in order to achieve efficient, economical stroke variation a totally new configuration of engine is necessary, without the constraints of working within the bounds of existing engine concepts.
For this reason the "wobble plate" design was selected as a base from which to develop the invention, in which the cylinders are oriented around, and parallel to, the engine longitudinal center line, with the pistons acting against a wobble plate supported by a thrust bearing against a swash plate inclined so as to cause the wobble plate to oscillate in response to piston movement, said thrust bearing being also attached to said swash plate and, in which, the oscillating motion of the wobble plate is translated into rotary motion by means of the reaction of said thrust bearing against said swash plate, which is carried on the face of a carrier plate.
The angle of this swash plate can be varied by operator command without causing the carrier plate to move out of its plane of rotation, which is at right angles to the longitudinal center line of the engine. Thus, by varying the angle of inclination of the swash plate and, consequently, the wobble plate, the stroke of the pistons is caused to be changed.
The design is so arranged, as shown in the drawings, as to change the stroke of the pistons by moving the "bottom dead center" equivalent position of the pistons towards the cylinder head, thus retaining a constant combustion chamber volume throughout all variations of stroke and compression ratio.
The optional use of the opposing face of the variable angle of inclination swash plate to provide, if required, the pumping element for the fluid output section of a hydrostatic type of transmission as shown in FIG. 2. (Sheet 2) offers further versatility to this approach, while a mechanical transmission output can be used as shown in FIG. 1 (Sheet 1).
The total volume of space occupied by, and the weight of this engine is considerably less than that of a similar maximum swept volume crankshaft engine as is the magnitude of inertial losses due to the drive of unnecessary mechanisms in other variable stroke engine concepts.
It is anticipated that this invention will provide very considerable fuel savings in the operation of vehicles, which is an advantage that is particularly relevant in view of the necessity to reduce energy usage, is simpler in construction and will further result in a reduction of engine wear due to the lower piston speeds and bearing surface rubbing speeds at the short stroke condition which will probably be, by reason of normal driving patterns, be in operation for a majority of running time.
It is further believed to reach these goals in a simpler and more efficient form than other, previously mentioned, current endeavors in this field, or other variations to conventional engines such as the cutting out of some of the multiple cylinders of a normal crankshaft engine.